Different problems can be present in the transport of a printing substrate web to an electrographic printing device. For example, problems occur when the printing substrate web is delivered from differently arranged sources, for example from differently arranged printing substrate web stacks or from another printing device or from different types of printing substrate webs (a printing substrate web of a different width, pre-folded). In order to prevent web tears or web loops of the printing substrate web that are too large, storage buffers for the printing substrate web are provided. In a printing device a storage buffer is also required in order to have a sufficient reserve of printing substrate web upon starting and stopping the printing device. In particular, due to the re-proofing calculated for the pages in the retraction required in the printing device (for example in color printing), based on the start ramp-up to reach the printing speed a reserve amount of printing substrate web must be held back in order to avoid a tearing of the printing substrate web.
It is known (for example WO 98/39691 A1 or U.S. Pat. No. 6,246,856 B1) to solve this problem with the aid of what is known as a dancing roller arranged in a reserve buffer, a roller resting freely directed on the printing substrate web. If a loosening of the printing substrate web (a sagging of the printing substrate web) occurs in operation, this is drawn by the weight of the dancing roller into the reserve buffer and a loop is therefore formed. For example, this can be executed (for example DE 10 2004 002 232.1-51) such that sensors scanning the loop are arranged in the reserve buffer, which sensors output sensor signals indicating the length of the loop that are used to control the transport of the printing substrate web.
U.S. Pat. No. 6,068,172 A describes an electrographic printing device with a printing substrate transport device. A drive unit (made up of two drive rollers 12, 13) that transport the printing substrate into the printing device are provided outside the printing device. The printing substrate web is supplied in the printing device via a tension spring to a pendulum and from there arrives via deflection rollers at the transfer printing station in which the toner images are transfer-printed onto the printing substrate. After the transfer printing station an additional drive unit is provided that draws the printing substrate from the transfer printing station. The printing substrate conveyed by the drive unit into the printing device is supplied, tensioned by the tension spring, to the pendulum. The drive unit is thereby controlled by the tension of the printing substrate since the wrap angle of the printing substrate around the rollers is changed depending on the tension of the printing substrate. Depending on this angle, the drive motor for the rollers is regulated such that the deflection of the pendulum is between the end positions of the pendulum.
A device with which paper sheets can be laterally aligned arises from U.S. Pat. No. 3,436,002 A.
US 2005/158099 A1 discloses a device that is arranged at the output of a printing device in order to prepare the printing substrate for the processing by a post-processing apparatus. The printing substrate is initially supplied to a buffer storage, and arrives from there at a smoothing device. The printing substrate is subsequently moistened in a moistening device and is finally cooled in a cooling device. The printing substrate is subsequently supplied to the post-processing apparatus.
JP 09 086742 A describes a paper transport device in which the paper web is extracted from a storage roll, is directed via a brake to a buffer consisting of a spring, and subsequently arrives at a feed unit. The goal is to keep the paper web tensioned at the start of the feed of said paper web. This is achieved in that a slack of the paper web is accepted by the buffer and is additionally braked before the buffer. The paper web is therefore supplied to the feed unit in a tensioned state.
EP 0 756 215 A shows a device with which a printing substrate web can be cleaned on both sides. For this the printing substrate web is directed in an S-shape past cleaning rollers.
U.S. Pat. No. 5,540,146 A describes a device with which a printing substrate web can be laterally aligned. The alignment occurs with the aid of a sensor that scans the edge of the printing substrate web. The printing substrate web is mechanically aligned depending on the scan signal.
DE 27 21 003 A discloses a transport device for a printing substrate web via which a deviation and a zigzag movement of the paper web during the feed can be corrected.
GB 2 023 553 A shows a buffer storage with a negative pressure chamber at whose floor is arranged a vacuum pump that generates in the chamber a negative pressure via which the paper web is drawn into the chamber. A drive unit for the paper web is provided at the input of the chamber (as viewed in the transport direction of the paper web). The drive unit is arranged at a distance from the chamber.
A buffer device for a belt with two buffer stores situated in series, between which is arranged a drive drum that can be driven in both directions, arises from GB 1 469 844 A. The buffer stores are realized as negative pressure chambers in which respective sensors for scanning the loop length are arranged.
U.S. Pat. No. 3,464,610 A describes a paper transport device with a vacuum chamber in which sensors to scan the loop length are provided. A vacuum source is arranged on the floor of the chamber. A channel in which a negative pressure is generated is provided in the outer wall over which the paper web is drawn (by a drive unit), via which negative pressure an air cushion is formed at the end of the channel and at the input of the vacuum chamber over which the paper web is directed to the drive unit.
A buffer for a belt arises from U.S. Pat. No. 4,199,766 A. The belt is drawn into the buffer by the force of gravity. A gas cushion exists at the floor of the buffer.
U.S. Pat. No. 3,829,080 A shows a buffer storage that operates with negative pressure. The vacuum source is arranged at the floor of the buffer memory. A channel via which an air cushion is formed under the paper web before this is supplied to the drive unit is provided in the side wall.
FR 2 385 627 A describes a chamber through which a belt is directed downward through an opening at the floor of the chamber. The chamber is executed at an angle at the floor.
US 2003/039496 A1 deals with a printing in which a buffer storage is arranged before the transfer printing station. Three sensors with which the loop length is scanned are arranged in the buffer storage. The unit is arranged at the input of the buffer storage.
U.S. Pat. No. 5,729,817 A describes a color printing device with buffer stores that are realized as loop pullers.
US 2003/188647 A1 shows a printing device that has at an input an input module with a tensioning device for the paper web.
A regulation for transport of a printing substrate web in an electrographic printing apparatus is known from DE 10 2004 002 232 A1 or the corresponding US 2005/158099 A1.
FIG. 1 shows the design of an electrographic printing device DR as it is described in, for example, WO 98/39691 A1 or U.S. Pat. No. 6,246,856 B1; WO 98/39691 A1 and U.S. Pat. No. 6,246,856 B1 are herewith incorporated into the disclosure. The printing device DR has a printing module M2 and a fixing module M3. Arranged at the input of the printing module M2 for a printing substrate web 10 is a feed module M1 for the printing substrate web 10.
The printing module M2 contains (as an example) two electrophotography units E1 and E2 of known design that respectively generate toner images of images to be printed on a photoconductor belt; these toner images are transfer-printed onto transfer belts T1, T2, there are collected upon color printing, and finally the toner images are transfer-printed from the transfer belts T1, T2 onto the printing substrate web 10. The functions of the printing module M2 can be individually learned from WO 98/39691 A1.
The toner images are fixed on the printing substrate web 10 (for example with the aid of radiation fixing) in module M3; refer also in this regard to WO 98/39691 A1.
The feed module M1 for the printing substrate web 10 is arranged in the printing device DR in WO 98/39691 A1 or U.S. Pat. No. 6,246,856 B1. It contains a reserve buffer VP with a loop puller 11 that collects a slack of the printing substrate web 10. This is particularly of importance in start-stop operation of the printing module M2 since it can therefore be prevented that the printing substrate web 10 tears. From the feed module M1, the printing substrate web 10 arrives at the internal transport path TW for the printing substrate web 10 within the printing module M2. The feed module M1 can receive new printing substrate web, for example from a printing substrate web stack (not shown in FIG. 1) or from a printing device arranged beforehand in a printing path as a source of the printing substrate web.
The feed module M1 according to FIG. 1 is part of the printing device DR and is adapted to the needs of the printing device DR. Therefore problems occur if the printing device is, for example, part of a printing path made up of multiple printing devices and the printing path is changed or different printing substrate webs are used.